Recent work in optomechanics, enabled by advances in optical micro cavities and nano-electro-mechanical systems, has shown tremendous potential for new classes of micro scale devices and phenomena.
Traditional methods for providing non reciprocal devices rely on magneto-optic media, optically active media, or electro-optic crystals. According to a non-reciprocal optical system based on magneto-optical gyrotropy, a forward propagating right circularly polarized mode can be transformed by the operation of time reversal to a backward propagating mode that is also right circularly polarized. In a non-reciprocal optical system based on electro-optic crystals, non-reciprocity can take the form of two-wave mixing and can incorporate a phase grating that can be displaced from a fringe pattern generated by two waves being mixed.